Need some help with browning out sps

[04V10]

Hey guys,

I was wondering if I could get some guidance on 2 pieces of sps that I have in my 20 gallon. I have another piece in there that is nice and green and has awesome polyp extension, however the other two not so much. When I bought them from the store they were nice and blue and pink in color, however in my tank they have browned out. I have had them for about 4 months and there is a bunch of growth on them and the polyps were looking good.

I have had them under radions since the beginning of August at 38% and figured that the extra light could help them out. So I upped the lighting to 45%. After doing that, the polyps would not come out on one of them, and the polyps were just visible on the other. I left them like this for about a week with no improvement in color or polyp extension. So I put the lights back to 38% and right away the polyps came out again.

I have another thread on here asking about dosing so I'm wondering if that is my issue but here are my params as of tonight.
pH 8.0
alk 6.8 - 7 dKH
Ca 400
Mg 1280
PO4 slight coloration in my test. (red sea test kit)
0 Nitrates

Would my params be causing any issues with the browning coloration in the tank?

I do run an HOB skimmer, an AC70 modded with a fuge with chaeto running lights 24hrs live rock and chemi pure elite. I have sufficient flow in the tank and the flow on the sps corals is strong (not too strong) and turbulent.

I do have some bubble algae in the tank and scrape the glass every 2-3 days of algae.

Do you think that it's the PO4 in the tank that is causing the brownish color? If so, what could I run to help drop this issue?

Any suggestions would be great. Thanks.